Process for preparation of photosensitive composition

ABSTRACT

A process for preparing a compound having the structure ##STR1## which comprises heating under acidic conditions a polyvinyl alcohol and a compound of the structure ##STR2## is a polyvinyl acetal, n is an integer from 1 to 6, 
     R is hydrogen or alkyl, 
     m is an integer from 1 to 6, 
     X is an anion, ##STR3##  is a divalent radical having the structure ##STR4## Y is a monovalent radical having the structure ##STR5##  wherein R 1 , R 2 , R 3  and R 4  are hydrogen, alkyl, alkenyl, alkoxy, aralkyl, substituted alkyl, substituted alkoxy, carboxy, carboxy ester, amino, substituted amino, amido, substituted amido, cyano, hydroxy, nitro, isocyanato, sulphonyl halide, sulphonic acid and halide, and may be the same or different, or R 1  taken together with R 2  is methylene-dioxy, and A is a formyl or acetal group.

This is a division of application Ser. No. 07/878,239, filed May 4, 1992, now U.S. Pat. No. 5,326,669.

FIELD OF INVENTION

The present invention relates to photosensitive polymeric materials suitable for the preparation of printing plates, photoetching and inks and to more particularly processes for the preparation of these materials.

THE PRIOR ART

Photosensitive resists can be suitable for a wide variety of uses, including the preparation of several types of printing forms, including screen printing resists, printing plates and resists for the preparation of various stages of circuit board manufacture, as well as UV curable inks and overprint varnishes.

Water soluble or water processable photoresist materials have several advantages, encompassing such aspects as safety in handling, cost, and ease of processing after exposure. Additionally, water soluble or water swellable photopolymer materials can be used in such diverse applications as the manufacture of color and black and white TV screens, and the immobilization of enzymes or living micro organisms. In the last mentioned application, it is an absolute necessity to utilize innocuous materials to prevent damage or destruction of the material under investigation during the immobilization stage.

Water processable systems that have previously been used in one or more applications mentioned above are as follows:

a) Dichromate sensitized water soluble colloids. The use of these materials is diminishing, due to their reliance on toxic metal salts which present severe safety and effluent handling problems as well as the limited shelf life that their "dark reaction" brings to the system.

b) Diazo resins. These are usually diazodiphenylamine/formaldehyde condensation products; they are often utilized in metal free form, and when mixed with a water soluble colloid such as polyvinyl alcohol, can produce excellent results. However, they are somewhat unstable, with a limited shelf-life (especially under warm moist conditions), and their photographic speed is rather slow.

c) Free radical initiated systems. These consist of an initiator capable of forming free radicals when irradiated with actinic light, one or more unsaturated monomers or oligomers that contain vinyl unsaturation, and a water soluble colloid. These systems have a double disadvantage of being both oxygen and moisture sensitive, which can lead to exposure speed variations. They can also be heat sensitive and polymerize when stored at elevated temperatures.

d) Photodimerizable materials. These have the advantage of being fast exposing, and unaffected by moisture, oxygen and heat. The water insoluble variety is best characterized by polyvinylcinnamate.

Water soluble resins based on a styrylpyridinium salt, possessing a formyl or acetal group which is utilized to react with polyvinyl alcohol and so produce a photopolymer that contains Photodimerizable substituents along the polymer chain, have been described, as have chalcone derivatives similarly attached to polyvinyl alcohol. The stilbene derivatives are usually more efficient than the chalcone types.

Photopolymers described in U.S. Pat. Nos. 4,339,524; 4,564,580; 4,272,620 and 4,891,300 and Euro Patents 0 313 220 and 0 373 537 utilize a stilbazolium quaternary based system. However, the connection point to the polyvinyl alcohol is via a formyl or acetal grouping attached to the styryl entity. This severely restricts the capability to modify the absorption characteristics of the chromophore, and hence, all photopolymer compositions within the "family." The styryl grouping makes such a major contribution to the absorption characteristics of the overall molecule, that having to restrict that component of the chromophore by using it as a connecting point to the colloid, drastically limits what advantageous substituents can be incorporated in that part of the molecule. It also places a very severe restriction as to what raw materials can effectively (and practically) be utilized to prepare a photosensitive resins of the particular type described by the aforementioned patents.

In the aforementioned U.S. and Euro patents the photodimerisable entity is usually converted into a salt form to endow the material with additional advantageous properties. However, the compounds disclosed in these patents are structurally very restrictive with regard to freedom of substitution, so they do not allow for the preparation of compounds having a wide range of desirable properties with respect to absorption, activity, solubility and cost.

THE PRESENT INVENTION

The present invention relates to a particular family of photopolymers that possess a high degree of photosensitivity as well as marked solubility in water.

In accordance with the present invention there are provided photosensitive polymer compounds of the structure: ##STR6## is a polyvinyl alcohol acetal, n is an integer from 1 to 6, preferably 1, R is hydrogen or alkyl, m is an integer from 1 to 6, preferably 1 to 3, X is an anion, ##STR7## is a divalent radical having the structure ##STR8## Y is a monovalent radical having the structure ##STR9## is a 5 or 6 membered heterocyclic ring in which Z is nitrogen, substituted nitrogen, oxygen or sulfur, and R₁, R₂, R₃, and R₄ are selected hydrogen, alkyl, alkenyl, alkoxy, aralkyl, substituted alkyl, substituted alkoxy, carboxy, carboxy ester, amino, substituted amino, amido, substituted amido, cyano, hydroxy, nitro isocyanato, sulphonyl halide, sulphonic acid, or halide and may be the same or different, or R₁ and R₂ may be joined to form methylenedioxy, ethylenedioxy, and the like.

the anion is prefereably inorganic and more preferably is halogen.

The alkyl groups in alkyl and alkyl containing groups such as for example, alkoxy and alkylamino preferably contains from 1 to 6 carbon atoms. The alkenyl groups preferably contain from 1 to 6 carbon atoms.

Representative compounds of this invention include compounds of the structure ##STR10## where R, R₁, R₂, R₃, R₄ X, m, n and ##STR11## are the same as above.

These compounds can be readily obtained by heating an acidic aqueous solution of polyvinyl alcohol with a compound of the formula ##STR12## where A is a formyl or acetal group and the remaining structures are as defined above.

The term "polyvinyl alcohol" refers to a saponified vinyl acetate polymer having a saponification degree of 70 to 99 mol %. Thus, if the starting vinyl acetate polymer is a homopolymer of vinyl acetate the content of the vinyl alcohol units is 70 to 99 mol %; i.e. a vinyl alcohol polymer having a vinyl alcohol content of 70 to 99 mol %. Accordingly, the content of the monomer copolymerizable with vinyl acetate, which constitutes the vinyl acetate polymer is restricted so that the above-mentioned value of the saponification can be given. It is preferred that the polymerization degree of the vinyl acetate polymer be from 300 to 3,000.

The above described intermediates used in the preparation of the polymeric products are conveniently prepared from readily available inexpensive bulk chemicals. For example, the reaction may be carried out as follows: ##STR13##

The resultant acetal contains a highly active chloro group, activated by the adjacent amide carbonyl. It is therefore a good "leaving" group and the subsequent salt forming reaction with a styryl base is very straightforward and easy.

A specific example of the reaction is as follows: ##STR14##

In addition to being able to easily mix the photodimerizable entities, the photopolymer can be further modified by the addition of non-light sensitive co-reactants during the condensation with polyvinyl alcohol to change the properties of adhesion, solubility, or resistance to solvents or water. Examples of such non-light sensitive co-reactants are acetaldehyde, its dialkyl acetal, chloroacetaldehyde dialkyl acetals, methylaminoacetaldehyde dimethyl acetal, propionaldehyde, sulfo benzaldehyde, dialkylamino benzaldehydes and glyoxyllic acid etc. The polyvinyl alcohol may be any partially or fully hydrolysed grade, and the photopolymers can be prepared by reacting the photodimerizable salt form of the styryl base in an aqueous solution of the polyvinyl alcohol in the presence of an acid catalyst. The reaction is usually carried out at a pH of around 2.0 using hydrochloric, sulfuric, phosphoric or an organic sulphonic acid. The reaction is usually carried out at about 70° C. for a period of 4-8 hours.

However, the time and temperature can be varied a great deal, if required. The photopolymer may be separated by precipitation in a suitable non solvent (e.g., acetone), used directly, or after the pH has been ameliorated by use of an ion exchange resin etc.

The current invention is particularly advantageous in that it allows the entire chromophore to be easily substituted with any group or number of groupings that can advantageously affect the absorption, solubility, activity or even cost of the photopolymer material. In the aforementioned U.S. and Euro patents the photodimerizable entity is converted into a salt form to endow the material with additional advantageous properties, the present invention makes use of a "connecting" entity (one that can react with polyvinyl alcohol) that forms a quaternary salt with the substituted styryl base. This permits freedom of substitution in the styryl ring, in fact the entire chromophore, permitting choice of absorption, activity, solubility and cost. Furthermore it is a simple process to isolate two or more derivatives with very different absorption characteristics and combine them to provide a broader spectrum sensitive product, increasing exposure speed with a wide variety of different exposure sources. The aforementioned patents are very restricted by comparison. The present invention affords water solubility by salt formation, where the entity that makes the salt is also the connecting point to the colloid.

Additionally, for the efficiency of the photoreaction, it is highly desirable that the exposed species (the entity remaining after the photo destruction of the chromophore) does not absorb a similar wavelength to the photoactive chromophore, and that the photoactive chromophore is rapidly destroyed by actinic light. This prevents the surface layer from self-screening or showing a "filtering" effect on the underlying layers.

The photopolymers characterized by the present invention have a very high photoefficiency, allowing thick layers of the photopolymer material to be hardened throughout the entire thickness of the coating, even with a relatively short exposure time to light of a suitable wavelength. They display a faster photospeed than diazo or other systems as described previously. The mechanism of cross-linking in this particular patent is by photodimerisation, and hence none of the photopolymers characterized by the patent, exhibit the susceptibility to oxygen, moisture and temperature of some other systems.

The photodimerizable chromophore need only be present in low concentration, less than 5 mol % based on the polyvinyl alcohol colloid, in order to provide high levels of photosensitivity. Consequently, many of the admirably properties of polyvinyl alcohol (its resistance to a very wide range of solvents, and its ease of degradation with low concentration of an aqueous solution of metaperiodate or bleach) are retained. The photopolymers described in the present invention are suitable for a very wide range of applications, and can be used in both photographic and photochemical processes where a resist, stencil or relief image is required, for example, as an etching resist for printing plates, and cylinders, name plates, dials, etc.: as resists for plating processes (preparation of printed circuit boards), as ink accepting images for lithographic plates, and as stencils for screen printing stencils. They may also be used in the preparation of photomasks for cathode ray tubes as used in both black and white and color television sets. They can also find use in the preparation of specialized water-based UV curable inks. As previously mentioned, the photopolymers characterized by the present invention can be very easily modified to cover a previously unprecedented range of wavelengths, making them suitable for use with a variety of different laser devices such as used in the direct scanning of lithographic printing plates.

The invention will become clearer from the examples which follow. These examples are given by way of illustration and are not to be considered as limiting.

EXAMPLE 1 N-2 -Dimethoxyethyl-N-methyl-chloro-acetamide

To a solution of 168 g. anhydrous potassium carbonate in 200 cc water were added with stirring:

    ______________________________________                                         Methylamino-dimethyl acetal                                                                          144 g.                                                   Ice                   400 g.                                                   Methylene chloride    400 g.                                                   A surfactant-triethylamine salt of                                                                    2 g.                                                    dodecylphenyl-sufonic acid                                                     (60% aqu. solution)                                                            ______________________________________                                    

To the resultant dispersion was added dropwise with stirring over a period of 30 minutes, a solution of:

    ______________________________________                                         Chloroacetyl chloride                                                                            142 g.                                                       Methylene chloride                                                                               100 g.                                                       ______________________________________                                    

During the addition 400 g. of ice was added portionwise to keep the reaction temperature below 5° C.

The stirring was continued for thirty (30) minutes after the addition was completed allowing the reaction mixture to reach ambient temperature. The organic layer was separated and the aqueous layer extracted three times with methylene chloride. The extracts and organic layer were combined and treated with activated carbon which was then removed by filtration. The organic solvent (methylene chloride) was removed under vacuum in a rotary evaporator leaving 234 g. of product as a pale yellow oil.

EXAMPLE 2 4-(4 -Methoxystyryl)-pyridine

A mixture containing:

    ______________________________________                                         4-Picoline              38 g.                                                  4-Anisaldehyde          55 g.                                                  Xylene                  400 g.                                                 Dimethylformamide       32 g.                                                  p-Toluene-sulfonic acid 32 g.                                                  ______________________________________                                    

was stirred under reflux for 24 hours using a Dean & Stark apparatus to remove water formed during the reaction. About 250 cc. of xylene/dimethylformamide were then removed by distillation. The residue was cooled and hexane then added with stirring. The solid was removed by filtration, washed with hexane, and air-dried. The solid was then dispersed in 1 l. water and the aqueous dispersion was heated to near boiling 28 g. anhydrous sodium bicarbonate was added portion wise with stirring. The mixture was kept near boiling and stirred for 2 hrs, the pH being checked to ascertain that the pH was alkaline, sodium carbonate being added if needed, and then filtered. The product was washed with water and air dried to yield 74 g. of a pale buff solid.

EXAMPLE 3 N-2-Dimethoxyethyl-N-methylacetamido-4-(3,4-dioxymethylenestyryl)-pyridinium chloride

A mixture containing:

    ______________________________________                                         4-(3,4-Dioxymethylenestyryl-pyridine                                                                     4.5 g.                                               Ethyl acetate             40.0 g.                                              N-2-Dimethoxyethyl-N-methyl-                                                                             4.2 g.                                               Chloroacetamide                                                                ______________________________________                                    

was stirred under reflux for 24 hours, cooled, filtered and washed with ethyl acetate. The product was air dried to give 6.8 g. of a yellow solid.

EXAMPLE 4 Condensation of N-2-dimethoxyethyl-N-Methylacetamido-4-(4-chlorostyryl)-pyridinium chloride with polyvinyl alcohol ##STR15## 500 cc boiling water were stirred vigorously to produce a good vortex, and 44.0 g. Vinnol brand of polyvinyl alcohol was added carefully to the vortex. Vinnol 540 is 87%-89% saponified polyvinyl acetate having a viscosity of 40-50 cps in a 4% aqueous solution at 20° C. Stirring was continued until a complete solution had formed and the temperature had dropped to around 65°-70° C. 8.0 g. of 85% phosphoric acid was then added followed by the addition of 8.2 g. of N-2-dimethoxyethyl-N-methylacetamido-4-(4-chloro styryl)-pyridinium-chloride.

A pale yellow solution quickly formed and stirring was continued at 65°-70° C. for 7 hours (pH was 1.8). The solution was cooled and water was replaced to provide a 10% w/w solution.

The solution according to Example 4 was coated onto 230 white polyester mesh, dried and exposed through a line test positive to five 2-unit steps (a unit being about 1.2 seconds) on a table top VNH fluorescent tube exposure unit. VNH is an exposure unit with fluorescent bulbs as a light source and is available from VNH Industries, Inc. On development with water, a faithful negative reproduction of the original line positive wash obtained with all exposure steps adhering to the mesh substrate.

Using the procedures given above compounds wherein the pyridine ring is replaced by other N-containing heterocycles may be prepared.

EXAMPLE 5

The procedure of Example 4 was repeated using 300 cc. boiling water and 22.0 g. Vinnol 540. Concentrated hydrochloric acid (1.5 g.) was used in place of the 85% phosphoric acid. The addition of the acid was followed by the addition of 4.1 g. N-2-dimethoxyethyl-N-methylacetamido-4-(4 -chloro-styryl)-pyridinium chloride and then 5.0 g. of 50% aqueous glyoxyllic solution. A pale yellow solution formed and the pH dropped to below 2.0. Stirring was continued at about 65°-70° C. for 8 hours and water added to provide a 10% w/w solution.

The solution was coated onto a white polyester mesh base and the coating permitted to dry, then exposed to UV light. The developed, dry film showed increased resistance to water while retaining all the solvent resistance of the unmodified material as well as to the degradability with bleach solution or metaperiodate ions.

EXAMPLE 6

    ______________________________________                                          ##STR16##                                                                     2-[4-Methoxystyryl]-Quinoline                                                  ______________________________________                                         Quinaldine            14.3 g.                                                  Anisaldehyde          13.6 g.                                                  Xylene                100.0 g.                                                 DMF                   8.0 g.                                                   PTSA                  8.0 g.                                                   ______________________________________                                    

Stirred above under reflux, [Dean & Stark conditions], after hours, a yellow/orange solid precipitated, accompanied by frothing and bumping. Continued refluxing for 12 hours, cooled and filtered. Added resultant solid to boiling water, stirred and carefully added sodium carbonate until well alkaline. Continued stirring [at near boiling] for 2 hours, checked still alkaline and filtered. Washed with hot water. Air dried, yellow solid Yield 16.9 grams.

EXAMPLE 7

    ______________________________________                                          ##STR17##                                                                     2-[4-Chlorostyryl]-Quinoline                                                   ______________________________________                                         4-Chloro-Benzaldehyde   14.0   g.                                              Quinaldine              14.3   g.                                              Acetic Anhydride        18.0   g.                                              Glacial Acetic Acid     9.0    g.                                              Stirred under reflux for 11 hours, then poured on to:                          Ice/Water               1.0    kg.                                             Stirred and added portionwise:                                                 Anhydrous Sodium Carbonate                                                                             15.0   g.                                              ______________________________________                                    

Stirred and heated to around 60° C. [PH alkaline], for 45 minutes. Filtered and washed with hot water. Oven dried buff granular solid. Yield: 25.1 g.

EXAMPLE 8

    ______________________________________                                          ##STR18##                                                                     4-[4-Hydroxy-3-Methoxystyryl]-Pyridine                                         ______________________________________                                                4-Picoline    38.0   g.                                                        Vanillin      61.0   g.                                                        Xylene        400.0  cc                                                        DMF           40.0   cc                                                        PTSA          32.0   g.                                                 ______________________________________                                    

Stirred under reflux [Dean & Stark conditions] for 7 hours, [solution becomes completely clear when approximately 7 cc of water has been collected]. The reaction solution then starts to become turbid as the product begins to precipitate. Continued hearing and stirring [under Dean & Stark conditions] for the total 7 hours, taking care not to overheat material [some decomposition will occur if the reaction mix is overheated]. Allowed to stand overnight, filtered, washed with hexane and then dispersed in hot water. Stirred and added portion wise to the hot stirred suspension:

    ______________________________________                                         Sodium Carbonate  10.0 g.                                                      ______________________________________                                    

PH after 2 hours of vigorous stirring was 7-8, filtered and washed with hot water. Air dried yellow solid. Yield: 86.2 g.

EXAMPLE 9

    ______________________________________                                          ##STR19##                                                                     4-[3-4-Dimethoxystyryl]-Pyridine                                               ______________________________________                                         4-Picoline              28.5   g.                                              3-4-Dimethoxy-Benzaldehyde                                                                             50.0   g.                                              Xylene                  300.0  cc                                              DMF                     24     cc                                              PTSA                    24     g.                                              ______________________________________                                    

Stirred under reflux for 24 hours, cooled and added hexane with vigorous stirring. Left over night and decanted off all the solvent. Dissolved up sticky solid in approximately 200 cc of hot methanol and poured resultant on to a stirred solution of:

    ______________________________________                                         8N Caustic Soda  500 cc                                                        ______________________________________                                    

Stirred for 1 hour, filtered and washed with hot water. Air dried pale brown solid. Yield: 60.0

EXAMPLE 10

    ______________________________________                                          ##STR20##                                                                     N-2-Dimethoxy-ethyl-N'-Methyl-Acetamido-4-[3-4-5-                              Trimethoxystyryl]-Pyridinium-Chloride                                          ______________________________________                                         4-[3-4-5-Trimethoxy-Styryl]-Pyridine                                                                       5.4    g                                           Ethyl Acetate               35.0   cc                                          N-2-Dimethoxy-ethyl-N'-Methyl-Chloroacetamide                                                              4.2    g                                           ______________________________________                                    

Stirred under reflux for 30 hours, cooled, filtered and washed with ethyl acetate, air dried buff solid. Yield: 8.8 g

EXAMPLE 11

    ______________________________________                                          ##STR21##                                                                     4-[4-Chlorostyryl]-Pyridine                                                    ______________________________________                                         4-Picoline               40 g                                                  4-Chloro-Banzaldehyde    56 g                                                  Acetic Anhydride         70 cc                                                 Glacial Acetic Acid      35 cc                                                 ______________________________________                                    

Stirred under reflux for 15 hours, poured on to water with vigorous stirring, filtered, washed with very hot water followed by hexane, air dried yellow solid. Yield: 68

EXAMPLE 12

    ______________________________________                                          ##STR22##                                                                     Condensation of N-2-Dimethoxy-ethyl-N'-Methyl-Acetamido-4-                     [3-4-Dioxymethylenestyryl]-Pyridinium-Chloride                                 with Gohsenol GH 23 [PVOH]                                                     ______________________________________                                         Boiling Water               400    cc                                          To the above, added the following with vigorous stirring:                      Gohsenol GH 23              22.0   g                                           When a complete solution had formed, and the temperature had                   fallen to about 70° C., added the following:                            Conc HCl                    1.5    g                                           Immediately followed by:                                                       N-2-Dimethoxy-ethyl-N'-Methyl-Acetamide-4-[3-4-                                                            2.4    g                                           Dioxymethylenestyryl]-Pyridinium-Chloride                                      ______________________________________                                    

A clear yellow solution quickly formed, [PH<2], continued stirring at 65°-75° C. for 7 hours, allowed to cool, and added water to give an approximately 10% w/w solution.

The solution so formed was coated on to 230 white polyester mesh, dried, and exposed through a line positive to 5, 5-unit steps [a unit being approximately 1.2 seconds] on a table top VNH fluorescent tube exposure unit. A good image formed after an easy washout. All steps adhered to the fabric. 

What is claimed is:
 1. A process for preparing a compound having the polymer composition of the structure ##STR23## is a polyvinyl acetal, n is an integer from 1 to 6,R is hydrogen or alkyl, m is an integer from 1 to 6, X is an anion, ##STR24## is a divalent radical having the structure ##STR25## Y is a monovalent radical having the structure ##STR26## wherein R₁, R₂, R₃ and R₄ are hydrogen, alkyl, alkenyl, alkoxy, aralkyl, substituted alkyl, substituted alkoxy, carboxy, carboxy ester, amino, substituted amino, amido, substituted amid, cyano, hydroxy, nitro, isocyanato, sulphonyl halide, sulphonic acid and halide, and may be the same or different, or R₁ taken together with R₂ is methylenedioxy, which process comprises heating under acidic conditions a polyvinyl alcohol and a compound of the structure ##STR27## wherein A is a formyl or acetal group and n, R, m, X, Y and -N are as previously set forth.
 2. A process according to claim 1, wherein the polyvinyl alcohol is a partially or fully hydrolyzed polyvinyl acetate.
 3. A process according to claim 2, wherein the reaction is carried out a pH in the range from 1.0 to 4.0.
 4. A process according to claim 3, wherein at least one non-light sensitive modifying compound containing a formyl or an acetal group is incorporated in the reaction mixture so as to also condense with the polyvinyl alcohol during the reaction.
 5. A process according to claim 4, wherein one or more of the modifying compounds is selected from acetaldehyde, acetaldehyde dimethyl acetal, acetaldehyde diethyl acetal, chloral, chloracetaldehyde dimethyl acetal, chloroacetaldehyde diethyl acetal. Methylaminoacetaldehyde dimethyl acetal, 4-dimethylamino benzaldehyde/sulfo benzaldehyde or glyoxyllic acid.
 6. A process according to claim 5, wherein the reaction is carried out in the presence of a catalyst selected from phosphoric acid, hydrochloric acid, sulfuric acid, p-toluene sulphonic acid, methane sulphonic acid, butane sulphonic acid, and benzene sulphonic acid.
 7. A process according to claim 6, wherein the reaction is carried out a temperature in the range 15°-100° C. and a time range from 2 to 100 hours.
 8. A process according to claim 7, wherein the reaction is carried out so that the photosensitive chromophore is present at a concentration from 0.5-20 mole % based on the polyvinyl alcohol.
 9. A process according to claim 8, wherein the ratio of the chromophore to the polyvinyl alcohol is 8.2 to 44.0 on a weight basis. 